Available-for-Sale Marketable Securities - Summary of Available-for-Sale Marketable Securities by Major Type of Security (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 162,796	$ 199,690
Gross Unrealized Gains	393	197
Gross Unrealized Losses	(461)	(27)
Estimated Fair Value	162,728	199,860
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,065	16,052
Gross Unrealized Gains	249	31
Gross Unrealized Losses		(2)
Estimated Fair Value	16,314	16,081
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,601	25,803
Gross Unrealized Gains	39	14
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	17,639	25,816
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	93,681	115,788
Gross Unrealized Gains	79	125
Gross Unrealized Losses	(460)	(23)
Estimated Fair Value	93,300	115,890
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	31,949	38,547
Gross Unrealized Gains	26	27
Gross Unrealized Losses		(1)
Estimated Fair Value	31,975	38,573
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,500	3,500
Estimated Fair Value	$ 3,500	$ 3,500